Rare earths are not a type of soil but rare minerals, which are an extremely important resource. Rare earths refer to 17 rare elements, including lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, and others.
How Were Rare Earths Discovered?
The discovery of rare earths began in the late 18th century when insoluble solid oxides were referred to as “earth.” Although rare earths are abundant in nature, they are generally separated in the form of oxides, making their extraction and purification challenging. As a result, they appear scarce and were thus named “rare earths.” The 17 rare earth elements were not discovered at the same time; from the discovery of yttrium in 1794 to promethium in 1947, the process spanned 153 years. Countries like China, Russia, the United States, and Australia hold leading positions in rare earth resource reserves.
How Are Rare Earths Classified?
Rare earths can be categorized based on different criteria:
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By Atomic Number
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Light Rare Earth Elements: Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm).
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Heavy Rare Earth Elements: Samarium (Sm) to Lutetium (Lu), including Yttrium (Y).
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Features:
Light rare earths are more common and widely used in large-scale industrial applications, while heavy rare earths are relatively scarce and better suited for high-tech fields.
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By Mineral Source
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Monazite-type Rare Earths: These primarily contain light rare earth elements, especially high in cerium and lanthanum, widely used in polishing powders and catalysts.
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Xenotime-type Rare Earths: Rich in yttrium and other heavy rare earth elements, mainly used in high-temperature superconducting materials and lasers.
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Fluorocarbonate-type Rare Earths: Predominantly light rare earths, with high cerium and lanthanum content in the ore, used in magnetic materials and chemical catalysts.
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By Chemical Form
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Rare Earth Oxides: The most common chemical form of rare earth elements, known for their stability, is mainly used in catalysts and ceramic materials.
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Rare Earth Metals: Refined rare earth metals have high conductivity and specific magnetic properties, used in alloy manufacturing (e.g., magnesium and aluminum alloys).
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Rare Earth Compounds: Including rare earth halides and hydrides, which are highly chemically active, and used in lasers and optical materials.
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Rare Earths as the “Vitamins of Industry”
This nickname is attributed to their unique properties. Rare earths possess excellent physical properties such as optical, electrical, and magnetic characteristics. They can combine with other materials to create new materials with diverse properties. The most notable function of rare earths is their ability to significantly enhance the quality and performance of other products. For instance, they substantially improve the tactical properties of steel, aluminum alloys, magnesium alloys, and titanium alloys used in tanks, aircraft, and missiles. Furthermore, rare earths are also lubricants for various high-tech fields, such as electronics, lasers, nuclear industries, and superconductors. Rechargeable batteries, mobile phones, computer memory, and DVDs all rely on rare earth elements for proper functioning.
Unique properties:
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Magnetism: Neodymium, praseodymium, and samarium are used to produce high-performance permanent magnetic materials.
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Catalysis: Cerium and lanthanum are key components in automotive exhaust purification catalysts.
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Optical Performance: Europium, terbium, and yttrium are indispensable as luminescent materials in displays and LEDs.
Rare earth oxides or processed rare earth concentrates can be used as polishing powders widely applied to optical glass, eyeglass lenses, cathode-ray tubes, oscilloscopes, flat glass, plastics, and metal utensils. Adding rare earth oxides can produce optical glasses and specialty glasses for various purposes, such as infrared-transmitting glass, ultraviolet-absorbing glass, acid- and heat-resistant glass, and X-ray shielding glass.
Apart from industrial applications, rare earths also play a role in agriculture. Extensive research has shown that using rare earth elements in appropriate concentrations can enhance the absorption, transformation, and utilization of nutrients by plants.
Uses of the 17 Rare Earth Elements
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Lanthanum: Used in alloy materials and agricultural films.
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Cerium: Widely applied in automotive glass.
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Praseodymium: Extensively used in ceramic pigments.
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Neodymium: Widely used in aerospace materials.
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Promethium: Provides auxiliary energy for satellites.
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Samarium: Used in nuclear reactors.
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Europium: Used in lens manufacturing and LCD screens.
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Gadolinium: Applied in medical MRI imaging.
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Terbium: Used in aircraft wing regulators.
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Erbium: Used in military laser rangefinders.
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Dysprosium: Used as a lighting source in film and printing.
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Holmium: Used in the production of optical communication devices.
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Thulium: Applied in clinical diagnostics and tumor treatments.
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Ytterbium: An additive in computer memory components.
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Lutetium: Used in energy battery technology.
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Yttrium: Used in wire manufacturing and aircraft structural components.
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Scandium: Commonly used in alloy production.
Conclusion
Rare earth metals are ubiquitous and often overlooked, yet they are the silent drivers shaping technology, industry, and environmental landscapes.